In the study of subcortical structures that are brought into play with the propagation of paroxysmal activity from a penicillin focus in the motor cortex of the monkey, a question of importance is: In what way are neuronal aggregates essential to the full development of the experimental focal seizure? In seeking an answer, neuronal blockade of structures with previously demonstrated involvement was brought about by a stereotactically controlled cryoprobe. The instrument at hand permits graded cooling at its tip that is 0.1 cm in diameter and monitored by a microthermocouple. By using destructive degrees of cooling in selected subcortical areas, principally the ipsilateral globus pallidus, the progression of the paroxysmal activity was not affected. The results from the above have been published and the project completed.